the Miniature Turbojet Engine Rendered in 3D

[larry cottrill]

Forrest -

In this case, you're making it too complicated. A real draftsman draws a perfect hexagon by simply "walking" the compass (still set to the radius) around the circle. This is because he already knows that the chord of the 60-degree arc is exactly the radius of the circle.

There is also a method for making a "sensibly perfect" 5-pointed star without measuring angles, but I can no longer remember it, though I have done it long ago. I used to have an old booklet (circa 1940) that had all sorts of nifty drafting tricks that were great time-savers. Of course, most of these techniques are obviated by digital drafting tools.

L Cottrill

[WebPilot]

In this case, you're making it too complicated. A real draftsman draws a perfect hexagon by simply "walking" the compass (still set to the radius) around the circle. This is because he already knows that the chord of the 60-degree arc is exactly the radius of the circle.

Given only the dimension across the flats, we know neither the requisite
radius of the circle, nor the chord. This puzzled me why the draftsman
of the plans gave this dimension instead.

It would be an easy problem if they gave the dimension of the flat, but
they didn't. It would be easier still if I allowed the use of an angular
measurement device, but since

Pretend you have only a straight edge and compass (neither protractor,
nor triangles).

I made the problem even more difficult, ... but challenging.

I showed one way of how it can be accomplished.

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Now it's easy to finish drawing the hexagon having graphically
determined the necessary radius.

At e, draw a circle of radius rec. Notice where it intersects the circle
drawn at c. Label one of these points, f. Draw the line segment,
ef. This is a flat.

At f, do the same. Continue drawing circles and flats in succession
about the circle centered at c.



(c.t.)

I had forgotten how 'pretty', geometrical solutions can be.

PS:
I still use drafting instruments from time to time. Considering the cost
of printer ink and paper, I feel it is sometimes 'cost effective' to still
use them - especially if I have a "B" size drawing.

(c.t.)

[Jim Berquist]

God I wish things was so simlpe!
1,2,3,4,5, and home to 6!

Why not just set the angles?

[WebPilot]

Why not just set the angles?

Yes, you can do it that way, but you must first
compute the radius from the given 'across the
flats' dimension.

Now this can be done if you can draw a line making a
30° angle with the horizontal through the midpoint and
intersecting the left vertical line.

Or you can use trigonometry and a calculator (anyone
ever here of 'trig tables'?) and compute the radius:

radius = (d/2) / cos 30°

My problem was I didn't know if the software I use for a
'sketchpad' had the capability to 'rotate' objects or groups
and thus allow me to input an angle. Thus, I had no 'software
protractor' and could not draw a '30° line'.

I felt using trig and a calculator was 'cheating'.

Well, I thought to myself, "can I do it some other way?"

I wondered if I could do it graphically. When I figured out this
way to do it, I decided to post the method. It does work.

I hold the aircraft designers of WWII and before in high esteem
since they designed those beautiful airplanes with nothing more
than 'drafting instruments', slide rules, adding machines and
some paper, pencil and ink pens.

They displayed a vast degree of ingenuity.

While doing this, I felt for a brief moment, just like one of them.

(c.t.)

[WebPilot]

I used the 'sketchpad' to do the vector graphic and pasted
it into the drawing.

[WebPilot]

Just a start ...

[WebPilot]

Adding a little more detail ...

[WebPilot]

This is where we are.

[WebPilot]

Beginnings of the transverse tube ...

(c.t.)

[WebPilot]

et tu, Bruté ?

(c.t.)

painting by Vincenzo Camuccini, Mort de César, 1798

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

now rotate the piece ...

[Irvine.J]

I"m looking but I don't see it, what are we looking for in this picture after rotation?

[WebPilot]

James,

The axis of the transverse piece in the previous pic is no longer
perpendicular to the vertical axis of the threaded piece.

Now translate the new piece into position ...

(c.t.)

[WebPilot]

Now one way to attach the piece is to 'notch' it and silver
solder it to the threaded piece. This was drawn by using
the BOOLEAN feature.

Now that I step back and look at it again, there may be
a better and stronger way.

[WebPilot]

This I believe will result in a stronger joint, but will be more
difficult to accomplish.

Drill or mill a hole at the proper angle to a depth just enough
to allow the additional piece to 'slip fit' into the collar joining
the threaded portions.

[WebPilot]

While you are 'drilling', do not forget to do the fuel passage ...